How to test install flow?

I did a test project following the steps described. Everything went well, but when I click on Test Install Flow button it gives me "Need Admin Permission! You do not have privilege to install this application. Please contact your domain admin or directly sign-up on application provider website."

What am I missing?

Added the printscreen: enter image description here

Solution

Solved misteries. My google account was not set as admin for my domain.